Arthroscopic treatment of bilateral mandibular condylar cysts and associated osteoarthritis of the temporomandibular joints in a horse

A horse was presented with a history of unpredictable behaviour under saddle to the point that the owner deemed the horse dangerous to ride. In addition, at rest the horse frequently protruded his tongue and during mastication a "clunking" sound could be heard. Radiographic examination at a previous clinic had revealed a normal left temporomandibular joint (TMJ) and a radiopaque mass in the right TMJ. However, despite arthroscopic surgery of the abnormal joint, the clinical signs had not resolved. Diagnostic investigation at the referral clinic revealed that TMJ analgaesia altered both a baseline hindlimb lameness and a behavioural component to the movement of the horse. Computed tomography (CT) illustrated the presence of bone cysts within the mandibular condyles and marginal osteophytosis of the discomandibular joints consistent with osteoarthritis. Arthroscopic examination, debridement of the affected joints and post-operative intra-articular injection of autologous protein solution resulted in temporary resolution of both the behavioural changes and the "clunking" sound. Ultimately, the horse was euthanised for continued dangerous behaviour, which treatment had failed to resolve in the longer term. In conclusion, the presence of cysts in the mandibular condyle and osteoarthritis can be a cause of abnormal behaviour, which may render a horse dangerous to ride. The case report illustrates the complex interaction between the TMJ, behaviour and movement.